Self-Assembly of Tetraphenylethylene-Cored Metallacycles Linked by Stereo-isomerizable Ligands: Photo-induced E to Z isomerization within Supramolecular Structures

Abstract

A new series of [4+4] and [2+2] supramolecular metallacycles incorporating di-1H-pyrazole ligands based on tetraphenylethene (TPE) inspired us to gain an understanding of the successive photo-induced transformation of multiple TPE units within controlled metallasupramolecular architectures. Stereoisomers of TPE derivatives functionalized with di-1H-pyrazole modifiers H2Z and H2E as ligands were successfully synthesized. Coordination-driven self-assembly of the ligands H2E/H2Z with di-Pt(II)/di-Pd(II) yielded [4+4] metallacycles ([E-Pd]/[E-Pt]) and [2+2] metallacycles ([Z-Pd]/[Z-Pt]). Photo-induced E→Z and Z→E isomerization of the di-1Hpyrazole ligands within these organometallic supramolecular assemblies facilitated the conversion between [4+4] and [2+2] metallacycles. Notably, complete isomerization of the E-TPE derivative into its Z-isomer via metallosupramolecular assembly could not be achieved by irradiation or heating of the free TPE-based di-1Hpyrazole ligand.